When a 64 byte 802.1q tagged Ethernet framed is received over a trunk port on a L2/L3 6509 and is routed/forwarded to an untagged access port the 802.1q tag is reduced and frame size reduced by 4 bytes. Should the 6509 switch be adding the additional 4 bytes of padding to meet the ieee 64 byte spec minimum OR should the originating host pad to 68 bytes so that the frame remains valid after removing tagging. I've read the 802.1Q IEEE spec and find the information somewhat contradictory.
This is not hypothetical, I actually have a device transmitting 64 byte tagged frames as described that are being dropped by the switch. I've attached an inline network tap and can see the frame being transmitted over the wire however a sniffer connected to a span port on the 6509 does not record the frame, it simply appears as though it's never been received. In addition there are no errors on the port including runts.